1. FIELD OF THE INVENTION
The present invention relates to a process for color photographic processing and, more particularly, to a process for color photographic processing using a color developer which is stable even in the presence of heavy metal ions.
2. DESCRIPTION OF THE PRIOR ART
In the field of color photography, cyan, yellow, magenta or like couplers are incorporated in a silver halide emulsion using various methods, and coated on a support to prepare a color photographic material, which is image-wise exposed and subjected to a series of photographic processing steps for forming images therein.
The fundamental steps in photographic processing are a color-developing step and a silver-removal step. In the color-developing step, silver halide in an exposed silver halide color photographic material is reduced with a color developing agent to form a silver image and, at the same time, an oxidized color developing agent reacts with the couplers to provide dye images. Then, the color photographic material is subjected to a silver-removal step to oxidize the silver formed in the preceding step with an oxidizing agent (usually called a "bleaching agent"). The thus oxidized silver is then dissolved wth a complexing agent for silver ion usually called "a fixing agent" to remove the silver from the photographic material. Thus, the photographic material contains only dye images. In practical development processing, auxiliary steps are involved, in addition to the above-described fundamental steps of color development and silver removal, for maintaining the photographic and physical properties of the images or for improving the storage stability of the images.
For example, the steps of a hardening bath for preventing the light-sensitive film from being softened too much during processing, a stopping bath for effectively stopping the development reaction, an image-stabilizing bath for stabilizing the resulting images, and a delamination bath for removing a backing layer of the support are illustrative of these additional steps.
Developing agents used in a color developer are generally aromatic primary amines, in particular, p-phenylenediamine derivatives. Typical examples thereof include N,N-diethyl-p-phenylenediamine, 4-diethylamino-2-methylaniline, 2-methyl-4-[N-ethyl-N-(.beta.-hydroxyethyl)amino]aniline, 2-methyl-4-[N-ethyl-N-(.beta.-hydroxyethyl)amino]aniline, etc.
A large amount of sulfite cannot be used as a preservative (antioxidant) in a color developer containing these aromatic primary amines as developing agent in contrast to the situation with a black-and-white developer containing an N-alkyl-p-aminophenol or hydroquinone as a developing agent. The reason is a large amount of sulfite seriously inhibits the coloration reaction between the aromatic primary amine developing agent and the color coupler. Therefore, in a color developer containing an aromatic primary amine as a developing agent, hydroxylamine is generally used as an antioxidant together with sulfite. However, serious decomposition of hydroxylamine occurs in the presence of a slight amount of heavy metal ion, for example, iron ion or copper ion. Therefore, in a color developer containing hydroxylamine as a preservative, a sequestering agent for heavy metal ions is indispensable.
Aminopolycarboxylic acids, such as nitrilotriacetic acid, ethylenediaminetetraacetic acid, etc., are known as sequestering agents for heavy metal ions. However, they have the defect that they themselves accelerate the decomposition of hydroxylamine. 1,3-Diamino-2-propanoltetraacetic acid described in U.S. Pat. No. 2,875,049 and diethylenetriaminepentaacetic acid described in U.S. Pat. No. 3,462,269 are not satisfactory, although they cause hydroxylamine to decompose to a comparatively lower extent. Therefore, a chelating agent which can be used as a replacement for aminopolycarboxylic acids has been desired.
As a chelating agent other than aminopolycarboxylic acids, organic phosphonic acid compounds are disclosed in West German Patent Application (OLS) No. 2,227,639. However, these compounds do not possess sufficient masking ability for heavy metal ions. In addition, the masking capability for calcium ion is also insufficient. Further, since they form chelate compounds with calcium which are slightly soluble in water, the presence of calcium ion in a developer would lead to formation of a precipitate. The above-described organic phosphonic acid compounds contain phosphorus in such a large amount that, when discharged in waste water, they increase the phosphorus content in rivers and the sea and thus result in pollution. Therefore, a chelating agent which possesses a large masking power for heavy metal ions and calcium ion, which does not form any precipitate with calcium ion, and which pollutes nature due to phosphorus to a lesser extent has been desired.